1. Field of the Invention
This invention concerns directional fluorescent lamps. A directional fluorescent lamp comprises a tubular glass envelope having an electrode at each end, a phosphor coating on the envelope wall to convert the ultraviolet radiation from the low pressure mercury arc to visible radiation, and a reflector coating on a major portion of the envelope wall. The light is transmitted through that portion of the envelope wall which is void of reflector coating.
One example of a directional fluorescent lamp is an aperture lamp in which neither the phosphor nor the reflector covers the entire envelope, thereby leaving a longitudinal window through which most of the light is emitted. Examples of aperture lamps are shown in U.S. Pat. Nos. 3,067,356, 3,225,241, 3,717,781, 3,809,944, 3,875,454, 3,875,455 and 3,886,396.
2. Description of the Prior Art
There are three types of coatings that are commonly used in fluorescent lamps, in addition to the phosphor coating.
First, there is a protective coating used to prevent or reduce solarization as discussed in U.S. Pat. No. 3,676,729. Such coatings are transparent to visible light and can comprise the oxides of titanium, aluminum, silicon, zirconium, hafnium, niobium, tantalum, antimony, tin, boron and indium as disclosed in U.S. Pat. Nos. 3,067,356, 3,377,494, 3,541,377, 3,624,444, 3,676,729, 3,875,454 and 3,890,530.
Second, there are electrically conductive coatings used to aid lamp ignition. Such coatings are transparent to visible light and can comprise tin oxide or indium oxide as disclosed in U.S. Pat. Nos. 3,624,444 and 3,809,944.
Third, there are reflector coatings to reflect the light in a particular direction. Such coatings can comprise the oxides of titanium, magnesium or zinc as disclosed in U.S. Pat. Nos. 3,115,309, 3,225,241 and 3,379,917.
The prior art does not disclose or suggest the use of dark, nonreflective, light-absorbing coatings in fluorescent lamps. The FIGURE is a cross sectional view of a directional fluorescent lamp.